<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <style>
        .parent{
            height: 1000px;
            width: 300px;
            margin: 0 auto;
            padding: 30px;
            background-color: gray;
        }
        .red{
            height: 300px;
            width: 250px;
            border-radius: 50%;
            margin: 15px;
            background-color: red;
        }
        .green{
            height: 300px;
            width: 250px;
            margin: 15px;
            border-radius: 50%;
            background-color: green;
        }
        .yellow{
            height: 300px;
            margin: 15px;
            width: 250px;
            border-radius: 50%;
            background-color: yellow;
        }
    </style>
    <div class="parent">
        <div class="red"></div>
        <div class="green"></div>
        <div class="yellow"></div>
    </div>
</body>
</html>